The field of the invention relates to closures for capillary tubes and their assembly to such tubes.
Capillary tubes are small tubes designed for drawing liquid by means of capillary action and retaining such liquid through surface tension and adhesion. They are commonly used for drawing samples of blood, chemical solutions and suspensions, and other such materials. For many applications, the tubes are about several inches in length, five millimeters or less in diameter, and have volumes from about ten to five hundred microliters.
Blood samples can be taken with a capillary tube by making a small puncture in a person's finger and then moving an end of the tube into contact with the drop of blood which forms upon the finger. The blood is drawn into the tube by capillary action. Alternatively, a blood sample can be taken with a syringe and later divided into smaller volumes for testing by inserting the end of one or more capillary tubes into the sample. For convenience, and if an exact metering of the sample is required, material may be directly aspirated into the capillary tube using a mechanical pipetter.
Certain tests require that a liquid sample within a capillary tube be centrifuged in order to determine the percentage of solids within the sample. Quantitative buffy coat analysis, for example, involves the use of a precision-bore glass capillary tube which contains a solid plastic float. Upon centrifugation, the plastic float floats on top of the red blood cells and expands the lengths of the buffy coat layers. Dyes which will later be taken up by specific nucleoproteins may be coated upon the capillary tube, thereby allowing the buffy coat layers to be distinguished.
One end of a capillary tube must, of course, be closed prior to mounting it within a centrifuge. Clay has been used to seal capillary tubes, but such seals require careful handling and do not provide a good interface with the sample to be analyzed. Since measuring the height of the liquid sample within the tube may be important, a sharp interface is desirable.
Plastic stoppers or caps are preferable to clay seals formed at the ends of capillary tubes from the standpoint of providing a sharp interface. However, they too must generally be applied after a sample has been taken. Great care must accordingly be exercised so that a large part of the sample is not lost. Application of the stopper may be difficult due to the small sizes of the stopper and capillary tube.